DISORDERED STRUCTURE OF NA2CO3 AT 400-DEGREES-C

The structure of Na2CO3 at 400°C has been refined from a neutron powder diagram. Also, the line-widths have been measured in a high resolution X-ray powder diagram. The broadened lines are shown to correspond to rod-like intensity distributions in reciprocal space. In the (a*, c*)-plane all reflections are sharp. Therefore, displacement fluctuations occur in the b-direction, which are strongly correlated in the plane perpendicular to the rod. A model is presented that qualitatively explains the observed character of the line broadening. In the structure refinement split atoms are introduced in order to described the anisotropic atomic distributions. The relation between the structure model and the observed line broadening is discussed. © 1979.